1. Field of the Invention
The present invention relates to a liquid crystal display device having a plurality of display panels, such as a sub-panel and a main panel and more particularly to achievement of a high quality liquid crystal display device.
2. Description of the Background Art
Liquid crystal display devices are widely used for various kinds of equipment such as personal computers, OA equipment, and TV sets because they have many advantages such as lightness, compactness and low power consumption. In recent years, the liquid crystal display device has also been used in mobile terminal equipment such as a mobile phone, a car navigation device and a game player. Such liquid crystal display devices include a liquid crystal display panel formed of a plurality of pixels and a backlight unit to illuminate the pixels.
Each of pixels includes a pixel electrode connected to a signal line through a thin film transistor (TFT), a counter electrode and a liquid crystal layer held between the pixel electrode and the counter electrode. A voltage is applied between the pixel electrode and the counter electrode and pictures are displayed. Recently, a mobile phone with a main display panel and a smaller sub-display panel has been widely used. The main display panel has characteristics such that picture resolution is high and the displayed color is robust. The sub-panel is provided to show not only limited information such as time or remaining amount of an installed battery but also a view of a camera.
Japanese laid open patent application No. 2007-114576 discloses a twin type display in which the main panel is connected to the sub-panel through a flexible printed circuit board and the two panels are arranged back to back with a back light unit interposed between the two panels. Common power and signals are applied to the sub-panel through common power supply lines and signal supply lines arranged in the main panel and extending to the sub-panel. In the above construction, if the main panel is not displayed and the sub-panel is displayed, only scan lines arranged in the sub-panel are driven and images in the sub-panel are displayed corresponding to signals applied to the signal lines. Though, the scan lines of the main panel are not sequentially driven and the switch elements of the pixels in the main panel are off, a leak current may be generated and result in a reduction in the display quality of the main panel.